This invention relates to an anti-syphon valve for marine fuel supply apparatus and particularly a gasoline supply apparatus in marine propulsion drives.
In one widely used marine propulsion drive, an inboard mounted internal combustion engine is housed within a suitable enclosure within the boat and coupled through the transom to an outboard pendant drive unit. The enclosure not only protects the operating personnel from the operating components and the engine from the external environments, but provides a high degree of sound proofing. A gas tank is built into the boat, either in the side of the boat adjacent the engine or in the forward or bow portion of the boat. A gas line connects the tank to the engine fuel pump. The fuel tank is often located above the level of the fuel pump. The fuel line at the fuel pump is generally a flexible line which may break, or in the event of a minor fire may burn open. The flow from the tank may continue, as a result of syphoning, into the boat bilge. This of course creates an extremely hazardous condition.
In order to prevent the above condition, a spring-loaded check valve is mounted in the gas line between the fuel tank and the engine. The spring-loaded construction requires a selected pressure differential across the check valve before flow starts; for example, 30 inches of fuel. This provides a simple, safe and reliable anti-syphon construction. Such an anti-syphon control is also approved by the United States Coast Guard and thus may be used. However, the pressure differential requirement of the valve promotes creation of a vapor lock under commonly encountered engine operating conditions on warm days and/or warm engine compartments.
Another Coast Guard approved structure includes a solenoid-operated needle-valve having an operating coil connected to the engine's ignition key switch for operation. The valve is normally held closed by a heavy spring such that no fuel can be withdrawn from the tank unless the valve is electrically energized. Such a valve structure must however include a manual override to provide for manually opening the valve. If the operating coil or electrical system should fail or malfunction, the valve closes and shuts down the fuel supply. Such valves avoid the vapor lock problems associated with the simple check valve. However, whereas the cost of a check valve unit may be on the order of three dollars, the cost of a solenoid valve is on the order of fifty dollars.